Question

I have a winform on which i want to allow the user to move a control.

The control is (for now) a vertical line : label with border and a width of 1.

The context is not very important but i’ll give it to you anyways. I have a background with some graphics and i’d like the user to be able to slide a guideline above the graphics. The graphics are made with the NPlots library. It looks something like this:
http://www.ibme.de/pictures/xtm-window-graphic-ramp-signals.png

If i can find out how the user can click and drag the label/line control around the screen, i can solve my guideline problem. Please help.

Answer 1

The code for this can get a bit complex, but essentially you will need to capture the MouseDown, MouseMove, and MouseUp events on your form. Something like this:

public void Form1_MouseDown(object sender, MouseEventArgs e)
{
    if(e.Button != MouseButton.Left)
        return;

    // Might want to pad these values a bit if the line is only 1px,
    // might be hard for the user to hit directly
    if(e.Y == myControl.Top)
    {
        if(e.X >= myControl.Left && e.X <= myControl.Left + myControl.Width)
        {
            _capturingMoves = true;
            return;
        }
    }

    _capturingMoves = false;
}

public void Form1_MouseMove(object sender, MouseEventArgs e) 
{
    if(!_capturingMoves)
        return;

    // Calculate the delta's and move the line here
}

public void Form1_MouseUp(object sender, MouseEventArgs e) 
{
    if(_capturingMoves)
    {
        _capturingMoves = false;
        // Do any final placement
    }
}